Optical coherence tomography (SS-OCT) for obtaining a tomographic image of a biographic body with a wavelength-swept light source as a light source of an interferometer has been conventionally known (refer to, for example, Patent Literatures 1 and 2). In such tomography, the light from the wavelength-swept light source is divided into reference light that is guided to a reference optical path and measurement light that is guided to a measurement optical path, the reference light reflected on a reference mirror disposed in the reference optical path and the measurement light scattered and reflected on the biographic body as a measurement target disposed in the measurement optical path are again synthesized to be superimposed, so that a time-varying spectrum interference signal (beat signal) is generated. This spectrum interference signal (beat signal) is detected by a detector, the beat signal is sampled at equal time intervals on a time axis, and this spectrum interference signal (beat signal) is Fourier-transformed, so that the peak of each frequency on a frequency axis is detected.
However, an inverse proportional relationship is established between the wavelength and the position corresponding to the depth of the biographic body. The wave number does not therefore linearly vary on the time axis. When a point-spread-function of the interference signal is obtained on the frequency axis by the Fourier transform, the waveform of the point-spread-function is distorted in accordance with an increase in a depth of the biographic body. As a result, the tomographic image information is deteriorated.
To solve such deterioration, Patent Literature 1 discloses a wavelength-swept light source that linearly varies the wave number on the time axis. The wavelength-swept light source includes an oscillator having an electric optical deflector, an interferometer that outputs, relative to interference light by the difference between two optical paths by traveling oscillation output light from the oscillator in two optical paths each having a different optical path length, an electric signal representing interference intensity containing an AC component of a frequency proportional to the variation in the wave number of the oscillation output light of the optical path length, an error signal generation circuit that generates a feedback signal for maintaining a constant frequency of the AC component of the electric signal, and a feedback controller having a control voltage generation circuit that generates corrected control voltage to be supplied to the electric optical deflector by applying the feedback signal to the gain relative to the lamp voltage signal.
Patent Literature 2 discloses that a spectrum interference signal is Hilbert transformed, phase information is obtained by obtaining an arc tangent of the ratio between the spectrum interference signal and the Hilbert transformed spectrum interference signal, a function representing time dependency of a sweep wavelength is obtained after the phase information is unwrapped, and calibration relative to the time dependency of a sweep light source is executed by using the time dependency of the sweep wavelength.